4-(Trifluoromethylsulfinyl)phenol or 4-(trifluoromethylsulfonyl)phenol having a nitro group or an amino group at the 2-position is an important compound as a production intermediate of agrochemical (for example, refer to Production process 17 of WO2013/018928).
A method of oxidizing 4-(trifluoromethylsulfanyl)phenol using a sodium tungstate catalyst is known in WO2009/133107.